The present invention pertains to the material handling conveyor art and, more particularly, to an improved pusher mechanism for use therein.
Pusher mechanisms of various types have long been used in material handling conveyor applications to sort boxes or similar uniformly sized and shaped articles onto accumulators or chutes. Recently, these devices have also been applied to the sorting of airline baggage, which baggage is characterized by its non-uniformity in size and shape. Unlike articles normally sorted on package conveyors, consecutive articles of baggage may vary significantly in size, weight, center of gravity and friction coefficient with the conveyor belt. Additionally, baggage articles tend to be more fragile and more easily damaged by automated handling equipment. Such damage may be physical damage to the bags contents as well as the bag itself or destruction of routing tags or labels, resulting in missorting and misrouting of the baggage.
In one prior art pusher mechanism, a paddle is moved with rectilinear motion transversely across the conveyor belt, thereby engaging and shoving the bag off of the belt. Such a system requires a time delay in the complete cycle to allow engagement of the object with the paddle face. This time delay becomes a significant part of the complete cycle time at high cycle rates resulting in excessively high paddle speeds. In addition, this prior art configuration has no component of motion parallel to the conveyor belt. The paddle speed must be quite high and slippage is likely between the object and the paddle face. Considerable opportunity for physical damage and missorting of the object results.
In a second type of prior art pusher mechanism, a single paddle is driven by a parallel link mechanism in a circular pattern across the conveyor belt. As with the system described above, this single paddle configuration requires a significant time delay for a complete cycle of operation. This system is superior to the rectilinear motion paddle arrangement in that there is a component of paddle motion parallel to, and in the same direction as, the conveyor belt over the second half cycle of operation. For an object approaching the mechanism on the near side of the conveyor, this advantage is negated by the first half of the cycle which has a component opposed to the belt flow. This tends to increase the slippage with resulting jams and missorts.
A third prior art pusher mechanism has dual paddles, with each paddle provided on the end of an arm which rotates on a center adjacent to the side of the conveyor bed. As opposed to the first two prior art mechanisms described above, this system, having two paddles moving in a semicircular pattern across the conveyor belt, does not require a time delay for engagement since the "working" paddle is returning to its home position "downstream" of the paddle preparing to push the next object. Paddle arm radius is approximately equal to the belt width and minimum object spacing on the conveyor belt is equal to the length of the paddle arm. Elimination of the requirement for engagement time as in the above-described systems permits slower pusher speeds for the same cycle rate. In addition, in this design a component of motion of the paddle in the direction of belt travel exists to a varying degree throughout the paddle travel.
The problems with this third prior art pusher mechanism are as follows.
Since object spacing is determined by the length of the paddle arm, high cycle rates result in excessively high conveyor belt speeds. In addition, the rotating paddle arm requires an excessively large clearance area in the space adjacent to the conveyor bed to contain the mechanism.
There is a long felt need in this art, therefore, for a high-speed pusher mechanism, i.e. high baggage rate at low conveyor speeds, which minimizes baggage damage and requires a minimum of space adjacent to the conveyor belt.